Trends in wetting behavior for Ag-CuO braze alloys on Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) at elevated temperatures in air

In the current study, Ag-CuO, a reactive air brazing alloy was evaluated for brazing Ba0.5Sr0.5Co0.8Fe0.2O(3-delta) (BSCF). In situ contact angle tests were performed on BSCF using Ag-CuO binary mixtures at 950 and 1000 A degrees C, and the interfacial microstructures were evaluated. Wetting contact angles (theta < 90A degrees) were obtained at short times at 950 A degrees C, and the contact angles remained constant at 1000 A degrees C for 1, 2, and 8 mol% CuO contents. Microstructural analysis revealed the dissolution of copper oxide into the BSCF matrix to form copper-cobalt-oxygen rich dissolution products along the BSCF grain boundaries. The formation of a thick interfacial reaction product layer and ridging at the sessile drop triple point indicate that the reaction kinetics are very rapid and that it will require careful process control to obtain the desired thin but continuous interfacial product layer.